The present invention relates to a method and apparatus utilized in a wireless communications system, and more particularly, to a method and apparatus of frame rate control in a transmitter in a wireless communication system.
Wireless Fidelity (Wi-Fi) Display specification is a standard for a Wi-Fi technology and used in a latency-aware application for streaming in a short distance, such as a wireless local area network (WLAN). In the Wi-Fi Display application, a connection is established between a source device and a sink device. The source device encodes video contents into encoded video bit streams and sends the encoded video bit streams to the sink device. The sink device further decodes the received video bit streams and recovers to the video contents. Therefore, a user can watch the video contents on a suitable display of the sink device for the user's purpose than a display of the source device. For example, a user shares a video from a notebook computer to a large screen television so that multiple people can comfortably watch the video on the television together. In this example, the notebook computer is the source device and the television is the sink device (assuming the television supports Wi-Fi Display specifications), and the source device transmits video contents to the sink device for playback on a display of the sink device.
Since the transmissions of the video bit streams between the source device and the sink device are wireless, throughput may vary with wireless channel conditions. When some of the video bit streams have collisions or loss, retransmissions are required to recover corruptions so that the throughput is decreased. For example, the throughput is decreased in a noisy or path-loss environment or decreased in a coexistence mode of Bluetooth and Wi-Fi technology.
Please refer to FIG. 1, which is a schematic diagram of a wireless communications system 10 according to the prior art. The wireless communications system 10 can be a Wi-Fi system. The wireless communications system 10 includes a source device 100 and a sink device 102. The source device 100 includes a frame generating module 104 and a source driver module 106. The sink device 102 includes a sink driver module 108 and a display 110. The frame generating module 104 is used for generating slices partitioned from a frame and sending the slices to the source driver module 106. The source driver module 106 further transmits the slices wirelessly to the sink driver module 108. The sink driver module 108 decodes the received slices and recovers the received slices to the frame. The display 110 finally displays the frame. However, if the slices from the source driver module 106 to the sink driver module 108 have collisions or loss due to noisy channels, retransmissions for the slices are required.
Please refer to FIG. 2, which is a schematic diagram of transmitting and receiving operations of the wireless communications system 10 according to the prior art. A frame FRM_A is generated by the frame generating module 104 and partitioned into slices SLE_A1-SLE_A4. The slices SLE_A1-SLE_A4 are sequentially transmitted from the source driver module 106 to the sink driver module 108. But the slice SLE_A3 is not received by the sink driver module 108, so the source driver module 106 performs a retransmission for the slice SLE_A3 with a lower rate. The slice SLE_A4 is therefore queued in the source driver module 106 accordingly. However, the frame generating module 104 does not know that the source driver module 106 does not finish the transmissions for the slices SLE_A3 and SLE_A4 and further generates a frame FRM_B and partitions the frame FRM_B into slices SLE_B1-SLE_B4 when a frame generating time TM_FG is reached. The slices SLE_B1-SLE_B4 are sent to the source driver module 106 and queued in the source driver module 106. Besides, the sink driver module 108 performs frame combination for a frame FRM_A′ when a frame combining time TM_FC is reached and the display 110 displays the frame FRM_A′, where the slices SLE_A3 and SLE_A4 are not successfully received by the sink driver module 108. Therefore, the display quality of the display 110 is degraded and the following retransmissions of the slice SLE_A3 and transmission of the slice SLE_A4 are useless for the combination of the frame FRM_A′.
As can be seen from the above, the retransmission of the slice SLE_A3 and the transmission of the slice SLE_A4 not only enlarge the latency between the transmissions of the frames FRM_A and FRM_B (i.e. between the transmissions of the slices SLE_A4 and SLE_B1) but are also useless for the combined frame FRM_A′ in the sink driver module 108, so that the following frame transmissions are affected accordingly. Therefore, it is necessary for the frame generating module 104 to know the transmission status of the previous frame and further adjust the frame generating rate to overcome the useless situation and avoid the extra latency.